The present invention relates to a drying machine for drying clothes or the like contained in a drying chamber.
A prior drying machine is disclosed in U.S. Pat. No. 4,738,034. In the disclosed drying machine, the drying machine comprises a heater for heating the air and a fan for supplying the heated air to a drying chamber within a drum. Since the water included in washed clothes is evaporated, and the humidified air is exhausted from the drying chamber, the clothes in the drying chamber are dried. The drying machine has a detector of degree of dryness of clothes in the drying chamber, also. When the drying operation of clothes progresses and the degree of dryness has reached a predetermined value, for example, 95%, the heater and the fan are deenergized, that is, the drying operation is completed.
General speaking, there are three stages in the drying operation, comprising an initial stage I, a middle stage II and a final stage III, as shown in FIG. 7. FIG. 7 shows the relation of the temperature of the air exhausted from the drying chamber and the time.
In the initial stage I, the air heated by the heater is supplied to the clothes, the temperature of clothes rises gradually, and the temperature of the air exhausted from the drying chamber rises gradually, also.
In the middle stage II after the initial stage I, the heat supplied to the clothes, that is, the heat supplied from the heater is equivalent to the heat needed for drying the clothes, so that the temperature of the air exhausted from the drying chamber is constant.
In the final stage III after the middle stage II, the heat supplied to the clothes is more than the heat needed for drying the clothes. Because the evaporation of the water included in clothes is substantially completed, and the heat absorbing water included in the clothes is minimal, the temperature of the air exhausted from the drying chamber increases rapidly.
In the prior arrangement, the heater and the fan work continually from the beginning of the drying operation to the end of the drying operation. The temperature of the air in the drying chamber becomes too high especially in the final stage III of the drying operation. As a result, in the case that clothes are made of a synthetic fiber, for example, acrylic fiber or polyester fiber, since the melting point of the synthetic fiber is relatively low, there is a problem that clothes shrink or the appearance of clothes are damaged, for instance, a feeling of touching clothes is tough, a luster of clothes is lost, a nap of the clothes is raised, and pilling may occur.
On the other hand, in the case that the clothes are made of a natural fiber, for example, cotton fiber, which includes water inside of the fiber as a characteristic of the natural fiber, there is a period II.sup.+, when the speed of the dryness of clothes is reduced, in the latter portion of the middle stage II. In the period II.sup.+, the water on the surface of the natural fiber has already been evaporated, the water held inside of the natural fiber comes to the surface thereof, and the water which come to the surface is evaporated. However, the speed of the water coming to the surface of the natural fiber is slower than the speed of the evaporation of the water coming to the surface, so the surface of the clothes becomes too dry. As the heated air is supplied to clothes continuously during the drying operation, the amount of heat supplied to the clothes is excessive. Therefore, the speed of the evaporation and the speed of water coming out from the inside of the natural fibers are not balanced. As a result, the natural fiber shrinks and the appearance of the clothes made with the natural fiber is damaged.